@aquilifer I decided to try placing counters and cabinets on a diagonal for myself, and I can see what you mean, I think, at least in part. For me, getting the counters to snap together in the first place was tricky (but do-able with auto-counters on and patience). Also, when placing them to the southeast or northwest, the counter backing shows up normally, but when placing them southwest or northeast, it doesn't. Also, even when using auto-counters, the game will not automatically place a corner piece as it does in a square room. When it came to the cabinets, they would not snap together at all in a diagonal room; had to be placed via ALT. Are these the same issues you had? If not, would you please detail yours?
Also, I'd like to understand how having larger counter and cabinet pieces would help with this (it reads like there is some math involved which I'm not super good at, so layman's terms please :p ).
Regarding your request for corner pieces with angles at 135 and 225, I can definitely see how that is really necessary for octagonal rooms, and I will add it when I update the index.